In a network consisting of a number of nodes and many links connecting the nodes, a flow setting request is issued in order to establish a flow between nodes (origin node and terminal node) through which data is transmitted from a terminal to a destination terminal. The term “flow” here means a flow of data, which can be translated into a “session” or a “path”. In response to the flow setting request, a route design system that operates on a Network Management System (NMS) that is connected to each node in the network and that manages the node determines the optimum route on the network and incorporates the flow into the determined route.
Conventional manners of determining an optimum route have proposed a scheme that determines the optimum route having a smallest sum of link costs based on the costs defined for the respective links according to an amount of traffic and an objective function (MIN{ΣiΣjLi, j}, where Li, j represents a link cost of a link from the node i to the node j) (see, for example, Patent Literature 1 and 2).
Here, a cost is a physical value that traffic processing of each flow costs each node, and is exemplified by transmission power, receiving power, a bandwidth of the link and a using fee of the line accompanied by using the link.    [Patent Literature 1] Japanese National Publication of International Patent Application No. 2005-518717    [Patent Literature 2] Japanese Laid-open Patent Publication No. 2003-338832
A node having a power-saving function, such as Adaptive Link Rate (ALR), that controls a processing rate depending on traffic generally undergoes stepwise power control as denoted in the example of FIG. 29 that controls to have power 0 W at traffic of 0 Mbps; power 0.1 W at traffic in the range of 0-10 Mbps; power 0.4 W at traffic in the range of 10-100 Mbps; and power 3.6 W at traffic exceeding 100 Mbps.
In a conventional route calculating system, a route of a newly request flow is calculated such that amounts of traffic or power consumption of the respective links are leveled based on the link costs of the network when the flow setting request is issued.
Here, description will now be made in relation to an example of a network of FIG. 30A. In this network of FIG. 30A, the link from the node A1 to the node C1 has a traffic volume (forwarding amount) of 110 Mbps and therefore has link power consumption of 3.6 W from the relationship of FIG. 29.
Here, a flow setting request of a flow from the node A1 to the node B1 of 10 Mbps is assumed to be issued in the network in the above state. The links of the route passing through the nodes A1, C1 and B1 have link traffic volume of 110 Mbps and 120 Mbps and link power consumption of 3.6 W and 3.6 W while the links of the route passing through the nodes A1, D1, and B1 have link traffic volume of 50 Mbps and 95 Mbps and link power consumption of 0.4 W and 0.4 W. Since the conventional manner selects a route having a smaller link traffic volume or smaller power consumption, the route passing through the nodes A1, D1, and B1 has been determined to be the route of the request flow.
If the route passing through A1, D1, and B1 is set for the route of the request flow, the link traffic volume are 60 Mbps and 105 Mbps and link power consumption is 0.4 W and 3.6 W. At that time, the link power consumption between the nodes D1 and B1 increases by 3.2 (=3.6−0.4) W.
In contrast, if the route passing through A1, C1, and B1 is set for the route of the request flow, the link traffic volume are 120 Mbps and 130 Mbps and the link power consumption is 3.6 W and 3.6 w, which are unchanged.
As the above, the conventional route calculation system has a problem that the route determined for the request flow has a possibility of increasing prospective power consumption.
Furthermore, the conventional route determination determines a route using constraints on using traffic for a link used by two or more routes as constraint condition. Such constraint condition does not clearly define an allowable level for using the network to ensure the End-to-End quality of each flow carried in the network. Therefore, the route would be calculated under tough constraint condition.
Another conventional manner of determining a route retrieves all the patterns of all candidate routes, considering the end-to-end quality of the respective flows having various route lengths and quality requirements. Unfortunately, such conventional manner has a problem that a route is determined, considering the relationship between the network state, such as a node processing amount and link traffic that are fluctuating, and flow quality influence.